This invention relates to packages comprising a novel dessicant composition.
Most people are familiar with the small bags or capsules of dessicant, often of silica gel or moisture absorbing inorganic salts, which are used in packages of pharmaceuticals, precision instruments such as cameras, or other items which require protection from moisture.
It is desirable to provide a less expensive or more convenient means for achieving the protection of the contents of these packages. Moreover, it is desirable to provide a type of dessicant that can be tailored not to respond to rapid, temporary increases in moisture handling and before placement in the package. Such response unnecessarily uses up the water-retaining capacity of the dessicant or, more realistically, requires that it be given special handling before dispensing into the package to be protected.
Attention has been paid to these problems in the prior art. U.S. Pat. No. 3,704,806 discloses a composition comprising zeolite dessicant held in an adhesive bond with an epoxy resin or phenol-formaldehyde resins. Such a composition is disclosed to be useful as a film or in coating form. A polyvinyl butyral is used to increase the moisture permeability of the resins.
Other inventors have suggested improved means for using of particulate dessicants. U.S. Pat. No. 3,326,810 discloses a bag which is formed of a microporous polyurethane bonding a nylon mesh to form a sheet material and sealing the sheet material to form a nondusting bag of dessicant. The pore size of the polyurethane is given as 40-60 microns. It is through the pores that moisture vapor reaches the dessicant.
In U.S. Pat. No. 3,301,788, Cummings discloses a dessicant pellet formed of dessicant powder bonded together within a polyvinyl alcohol matrix. The resulting product is a relatively dust-free dessicant pellet.
None of the above attempts to improve the convenience and efficiency of dessicant use provide a broadly-acceptable solution to dessicant users. The constructions tend to be too expensive, and the dessicant cannot be loaded into the suggested binder materials at high loadings without an excessively fragile structure being created. Moreover, most of the binders are either susceptible to degradation by moisture or other chemicals or insufficient moisture-vapor-transmission characteristics.